Expression of prospero-related homeobox 1 (prox–1) transcription factor and epithelial adhesion molecule (EpCAM) in a rat model of intrahepatic cholangiocarcinogenesis

Abstract

Deregulation of homeobox genes may give rise to tumorigenesis in target organs (1). Immuhistochemical studies have shown that the Prospero-related homeobox 1 (Prox–1) gene is expressed in mature hepatocytes but is not detectable in non-parenchymal liver cells (2). EpCAM is a surface marker on human hepatic stem/progenitor cells that is reported as absent on mature hepatocytes.However, hepatocytes (that have recently derived from hepatobiliary progenitors) are reported to have EPCAM surface expression in different cirrhotic livers (3). In the current study we investigated the expression pattern of Prox–1 in a rat model of damage, fibrosis, cirrhosis and intrahepatic cholangiocarcinoma (CC). Sprague dawley rats were given thioacetamide in drinking water (500mg/l) until they developed tumors (for 18 weeks). Control rats were given normal tap water. Animals were sacrificed, liver was removed and RNA was isolated for real time PCR. Cryostat and Paraffin sections were used for histopathology. The mRNA expression levels of Prox–1, Cytokeratin–19, and Epithelial Cell Adhesion Molecule genes were examined by RT-PCR.Immunohistochemical analysis of the normal liver revealed that Prox–1 is expressed in hepatocytes, while it could not be detected in EpCAM and CK–19 positive biliary epithelial cells. A co-expression of Prox–1 with CK–19 and EpCAM was found in proliferating ductular cells, which were located within the fibrotic tissue of the cirrhotic liver after 12 and 16 weeks of TAA administration. Immunohistochemical analysis of the CC tissue demonstrated Prox–1 positivity in CK–19 and EpCAM positive tumoral cells as well. Compared to the normal liver tissue, no significant up-regulation of the Prox–1 gene-mRNA expression could be found during the development of CC whereas an up-regulation of CK–19 and EpCAM could be detected. These data suggest that EpCAM and Prox–1 positive cells might be tumor initiating cells and Prox–1 might be involved in neoplastic changes of the biliary epithelium during cholangiocarcinogenesis.